Dual rotation propeller system



Aug. 27, 1946. R. M, GUERKE DUAL ROTATION FROPELLER SYSTEM 2 Shets-Sheet1' Filed Feb. 15, 1943 v I I 'llll I INVENTOR RALPH 7 1. GUERKE ATTORNEYK will) v Alig- 1 1946. I R. M. GUERKE 2,406,460

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DUAL ROTATION PROPELLER SYSTEM Filed Febr 15: 1943 v 2 Sheets-Sheet 2PROPgLLER RP M1 L6 I I PROPELLER RPM ATTORNEY Patented Aug. 27, 1946DUAL ROTATION PROPELLER SYSTEM 7 Ralph M. Guerke, Verona, N.J.,'assignorto Curtiss-Wright Corporation, a corporation of Delaware ApplicationFebruary 15, 1943, Serial No. 476,019

My invention relates to tandem propeller systems for aircraft.

My invention, in a prominent aspect thereof,

1 Claim. (Cl. 170135.5)

relates to a tandem propeller system wherein energy which is appliedaerodynamically from one propeller to the other and vice versa is notconfined to the propeller system. Dissipation of this energy occurs inthe manner hereinafter described to thereby substantially decreaseundesired vibration ofthe propellers included in the propeller system.

Various other objects, advantages and features of my invention willbecome apparent from the following detailed description.

My invention resides in the tandem propeller system, features andcombinations of the-character hereinafter described and claimed,

For an understanding of my invention and for an illustration of one ofthe forms thereof, reference is to be had to the accompanying drawings,in which:

Figure l is a side elevational view showing a tandem propeller system ofthe invention;

Fig. 2 is a vertical sectional view, partly in elevation, showing thepropeller system of Fig. 1;

Fig. 3 is a vertical sectional view, partly in elevation, taken on theline 3-3 of Fig. 2 looking in the direction of the arrows; and

Figs. 4 and 5 are graphs indicative of blade vibration amplitudes.

Referring to Fig. l, A represents an internal combustion engine such,for example, as one of the radial type which is suitable for operatingan airplane. A shaft I extends forwardly from the engine A through thenose plate'i! disposed at the forward end of the engine housingstucture, said shaft I also extending through and beyond a housing 3suitably secured, as by screws 4, to said plate 2.

Interiorly of the housing 3, the shaft I has the hub 50. of a bevel gear5 suitably secured thereto,

as by a screw 6, said bevel gear 5 meshing with and driving a pluralityof bevel pinions 'I secured, respectively, to shafts 8 radially disposedin the housing 3. As shown, the shafts 8 are supported by inner andouter rings 9 and Ill, the inner ring 9 being loosely supported onalined surfaces of the aforesaid hub id-and an adjacent hub I I a of abevel gear II corresponding with the bevel gear 5, and the outer ring IE! being suitably 'secured to the interior circular surface of thehousing 3. The hub Ila of said bevel gear II is suitably secured, as bya screw I2, to a sleeve I3 loosely mounted on the shaft I.

As stated, the shaft I extends beyond the housing 3 and the end sectionthereof has secured thereto a propeller hub I4. The sleeve I3, likewise,extends beyond the housing I and the end section thereof, between thepropeller hub I4 and the housing 3, has secured thereto a propeller hubI5.

In accordance with one form of the invention, the hub I 4 is of suchcharacter that it supports three propeller blades I6 spaced from eachother by angles of degrees, the blades l6 forming a propeller P2.Further, the hub I5 is of such character that it supports threepropeller blades I'I spaced from each other by angles of 120 degrees,the blades I'I forming a propeller P3. Obvi'ously, suitable mechanismmay be provided for controlling the pitch of the blades forming the twopropellers described above.

From a consideration of Figs. 1 and 2, it will be understood thatoperation of the .engine A effects rotation of the shaft I in onedirection. As stated, the bevel gear 5 is secured to said shaft I androtates therewith. Power from the bevel gear 5 is transmitted to thesleeve I3 by the bevel pinions I and the bevel gear II. Accordingly, thedirection of rotation of the sleeve I3 is opposite that of the shaft Iand said shaft I and the sleeve I3 rotate at the same speed. In View ofthe foregoing, it will be understoodthat the propellers P2, P3 rotate inopposite directions and at the same speed.

With respect to the invention of this applica- 7 tion, it shall beunderstood that the term aerodynamic excitation as used in thisspecification and in'the appended claims is'to be limited to thatexcitation which'is aerodynamically produced by a blade of one of thedisclosed propellers on a blade of the other propeller. During operationof the disclosed tandem propeller system and, responsive to thisaerodynamic excitation, moments and forces are developed in each of thepropellers P2 and P3.

Responsive to vibratory forces acting along the thrust axis ofthepropellers P2 and P3, the following conditions develop: First, when thehub of the forward propeller P2 exerts a forward vibratoryv force andthe hub of the rear propeller P3 exerts a backward vibratory force, the,forces transmitted along the shaft I and the sleeve l3, respectively,are balanced either entirely or partially, depending uponthe magnitudesof the forces involved, in the bevel pinions I between the bevel gears'5and .I I; second, when the hub 10f the forward propeller P2 exerts abackward vibratory force and the hub of therear propeller P3 exerts aforward vibratory force,'the forces trans- 1 tively.

mitted along the shaft land sleeve l3, respectively, are balanced eitherentirely or partially,

fdepending upon the magnitudes of the forces involved, inthe screws thelatter connecting the housing 3 to the nose plate in the mannerhereiinbefore described. If not balanced in this manner, the forces passfrom the nose plate 2 to the engine A and its mount where theyare'efiectively clamped.

As will be understood in view of the foregoing,

a corresponding action exists as regards the mothe engine and its mount.

When these forces and moments balance each other before reaching thenose plate 2, or equivalent, or in the screws 4, or equivalent, asdescribed above, the mode of vibration of the propeller sysltem isreactionless. applied aerodynamically from one propeller'to the otherandvice versa is confined to the propeller system and, hence, must bedissipated by that That is, the energy which is system with consequentliability of destructive damage thereto.

When the forces and moments do not balance each other completely, areactive mode of vibration of the propeller system is established. That1 is, energy which is applied aerodynamically from one propeller to theother and .vice versa is not confined to the propeller system and,hence, is damped by the engine and its mount.

As stated above,.the propeller system of inj ventioncomprises twothree-bladed propellers P2 andP3, In accordance with the invention; theblades I! of. the rear propeller P3 are thicker to substantial extentthan are the. blades l3 of the front propeller P2. As hereinafterexplained 1 in detail, the propeller system is of this character inorder that the two propellers P2 and P3 will become resonant, due toaerodynamic excitation, at substantially different rot'ative speeds,respecpropeller P2 may be thicker than the blades of line L3 representsthe natural frequencypf the f rear propeller P3 at various propellerspeeds. The line L6 indicates 6th order propeller excitation 1(fixpropeller R. P. M.) such 6th order excitation being thereaction'between both of the propellers P2 and P3. at R3 and said lineL6 intersects the line L2 at R2. The curves C3 and C2, Fig.4, indicatevibration conditions of the respective propellers P3 The line L3intersects the line L3 and P2 in response to aerodynamic excitation.Thus, the aerodynamic excitation of the propeller P2 on the propeller P3becomes resonant with thenatural frequency of the propeller P3 at R3,and the aerodynamic excitation of the propeller P3 on the propeller P2becomes resonant with the natural frequency of the propeller P2 at R2.

In the system as disclosed, the propellers P3 3 and P2 become resonant,due to aerodynamic ex :citation, at such different rotative speeds,respec- J tively, that the resonant periods of thepropellers .do notoverlap. As will be obvious from a consideration of Fig. 4, vibration ofthe front propeller P2 is small when the rear propeller P3 beeAlternatively, the blades of the front ments which are developed in eachof the pro- 1 pellers P2 and P3. In tandem propeller systems whichoperate in accordance with my inventiomthere is a struc- ;ture, such asthe nose plate 2 herein disclosed, "which receives unbalanced. forcesand/or mov ments and from which they are transmitted to propellersystem. Such energy is clamped by the engine and its mount.

Merely for purposes of explanation and without limitation of theinvention, the disclosed tandem propel-ler'system may be of suchcharacter that the rotative speed of the propeller P3 is approximately400R. P. M. when it vibrates at approximately 240%) cycles per minute tobecome resonant at E3, and the rotative speed of the propeller P2 isapproximately 500 R. P. M. when it vibrates at approximately 3000 cyclesper minute p to become resonant at B2. 4 As stated above, the inventioninvolves atan- Y dem propeller system wherein the blades of the 'nantconditions.

rear propeller are thicker to a desired extent than are the blades ofthe front propeller, this 'arhave the same thickness and theblades ofone of the propellers may be longer than the blades of theotherpropeller to such extent as may be desirable inorder to produce thedesired reso- Alternatively, the blades of the two propellers may beidentical, as regards thickness and length, each of the blades of one ofthe propellers having associated therewith a rib, not shown, these ribs,during operation of the tandem propeller system, serving to change theresonant conditions of the propellers P2 and P3 in the desired manner.Still further, the propellers P2 and P3 may be formed of differentmaterials, respectively. Thus, the blades of one of the propellers maybe hollow and formed from steel while the blades of the other propellermay be formed from solid aluminum Or the like.

In general, therefore, in accordance with my invention, one propeller ofthe tandem propeller system differs structurally from the otherpropeller in the sense that the blades thereof are longer or shorter,thicker or thinner, formed from different materials, etc.

Although the invention has been described in connection with a propellersystem comprising two three-bladed propellers, it shall be understoodthat the invention is not to be thus limited. Alternatively, forexample, the propeller system of my invention may comprise twotwo-bladed propellers, two four-bladed propellers, etc.

In Figs. 2 and 301 the drawings, I have shown a simplified arrangementfor producing rctative movement, in opposite directions, of thepropellers P2 and P3. As regards the arrangement shown, it shall beunderstood that the'shafts 8 may be fixed non-rotatably in position andthe bevelpinions l secured rotatively to the respective shaftsBinsuitable manner.

As known in the art, there are many arrangements for effecting rotativemovement in opposite directions of the two propellers of a tandempropeller system. It shall be understood that any of such knownarrangements as may be suitable may be substituted for the simplifiedarrangement illustrated in Figs, 2 and 3 of this application.

While the inventfion has been described with respect to certainparticular preferred examples which give satisfactory results, it willbe understood by those skilled in the art after understanding theinvention, that various changes and modifications may be made withoutdeparting from the spirit and scope of the invention and it is intendedtherefore in the appended claim to cover all such changes andmodifications.

What is claimed as new and desired to be secured by Letters Patent is:

A propeller system comprising propellers arranged in tandem formation,an engine, a shaft driven thereby for operating one propeller, a sleeverotatable on said shaft for operating the 6 other propeller, gearingdisposed between said engine and the propellers for rotating said sleeveoppositely as regards the rotation of said shaft, the ratio of thespeeds of rotation of said shaft and sleeve being fixed, one of saidpropellers having its blades thicker than the other and of asubstantially different resonant period from the other, whereby theirrespective resonant periods occur at substantially different rotativespeeds, eachof said propellers having the same number of blades as theother propeller and means for transmitting the unbalanced moments andforces resulting from aerodynamic excitation to said engine and itsmount, said means comprising a thrust-receiving member for said shaftand said sleeve, said thrust-receiving member being associated with saidengine.

RALPH M. GUERKE.

